First it was Saw & Chopper in Rogue One; then Bo Katan and Ashoka in Mandalorian. I'm not really counting Boba (Holiday special), Greivous and the ROTS clones (Tartovsky animation) because they were created for the films, just that the cartoons came out before the films were finished.
Basically looks like Jason Isaacs has been told by Lucasfilm to be quiet about something.
https://www.slashfilm.com/629049/jas...my-tongue-out/
Isaacs of course was the Grand Inquisitor in Rebels. His character was eventually killed off, with Vader, the other Inquisitors, and eventually Thrawn becoming the main villains for the Ghost crew later on.
So provided there's a possibility that he's going to play a live action inquisitor, wonder where that would be? Obi-Wan seems the most obvious choice, as the Inquisitors were active for a good chunk of the Pre OT era. Andor maybe?
There's a slight possibility he could show up in something post-ROTJ. The Star Wars monthly comic revealed that the Inquisitor's force ghost is around during the OT, where it fought Luke (although this seems to contradict the "redeemed" temple guard version from the temple arc in Rebels).